Which of the following explains why elements in column 17 (the halogens) are very reactive?

Their atoms contain three energy levels.

Their atoms need only one electron to complete their outer energy level.

Their atoms have large masses.

Their atoms contain the same number of protons as electrons.

Question

Which of the following explains why elements in column 17 (the halogens) are very reactive?

 Their atoms contain three energy levels.

 Their atoms need only one electron to complete their outer energy level.

 Their atoms have large masses.

 Their atoms contain the same number of protons as electrons.

anonymous · Answer

Okay, so the question is asking about "halogens." 

The halogens on the period table of elements all have 7 valence electrons. 
("Valence electrons" are the electrons on the outer shell of an atom. It's their outer energy level.) 

The highest number of valence electrons that an atom can have is 8. 

So, since the highest is 8, 
and halogens have 7, 
then that means that the halogens only need ONE more electron, in order to reach the maximum limit of 8. 

Does that make sense? 

That's why the halogens are so reactive. 

One example is NaCl, 
"sodium chloride." 

That's table salt. 

Na (sodium) has ONE valence electron. 
Cl (chlorine) has SEVEN valence electrons. 

Together, they make 8.

anonymous · Answer

what is the awnser ??

anonymous · Answer

I gave the answer in my explanation. Read it.